1. Field of Invention
The present invention relates to a method for making solar cells with sensitized quantum dot and, more particularly, to a method for making solar cells with sensitized metal quantum solar cells in the form of nanometer metal particles.
2. Related Prior Art
Environmental pollution has drawn the attention of the world. There are concerns about global warming caused by the emission of carbon dioxide after consuming fossil fuel for example. Environmentally, there is a need for cleaner energy.
On the other hand, fossil fuel is running out. The price for fossil energy is skyrocketing. Economically, there is need for alternative energy.
People around the world are exploring non-fossil energy such as solar energy, wind power, geothermal energy, fuel cells and bio-energy, intending to reduce the burden that we put on the environment and generating sustainable energy. Solar energy is promising for being clean and safe environmentally, sustainable and inexpensive economically and almost everywhere.
Silicon solar cells were invented in the Bell Laboratory, USA in the 1970s. Silicon solar cells are operated based on the photovoltaic effect of silicon semiconductors. Silicon solar cells convert sunlit into electricity at high photovoltaic efficiencies. However, there are problems with the use of silicon solar cells. Firstly, their production is complicated. Secondly, they are expensive. Thirdly, they are demanding about raw materials.
Dye-sensitized solar cells were invented based on nanometer crystals in the 1990s. Nanometer crystal films of wide band gap semiconductors are used in dye-sensitized solar cells. Nanometer crystal films include huge specific surface areas for attracting much photosensitive dye, thus forming semiconductor electrodes to convert sunlit into electricity. The photovoltaic efficiencies of dye-sensitized solar cells are high while the prices are low. It is very likely that dye-sensitized solar cells will replace silicon solar cells in the future.
In operation, the molecules of the dye of a dye-sensitized solar cell absorb sunlit so that their electrons jump into an exited state from a ground state and rapidly move to a semiconductor band, thus leaving holes in the dye. The electrons spread to a conductive base and then move to paired electrodes via a circuit. The oxidized dye is reduced by electrolyte. The oxidized electrolyte is reduced by receiving electrons from the paired electrodes. That is, the electrons are returned into the ground state. Thus, the circulation of the electrons is completed.
A key factor for the performance of the dye-sensitized solar cell is the speed of the electrons traveling to the semiconductor band after the photochemical reaction. A single-semiconductor nanometer crystal film electrode is problematic in transmitting electrons. There is no built-in electric field, unlike a bulk semiconductor. Moreover, the nanometer particles are too small to form any space charge layer between the nanometer particles and the electrolyte. The migration rate of the electrons is low, and the chance that the electrons and electric acceptors reunite is high. Therefore, the photovoltaic efficiency is low.
In Chinese Patent Application No. 01140225 published on 22 May 2002, disclosed is a nanometer crystal film solar cell related to a dye-sensitized solar cell as shown in FIG. 9 of the attached drawings of the present application. It includes an electrode 5. The electrode 5 includes a transparent conductive substrate 51, a nanometer crystal film 52 made of a wide band gap semiconductor and formed on the transparent conductive substrate 51, a metal ion-attracting layer 53 formed on the nanometer crystal film 52 and a sensitizer layer 54 provided on the metal ion-attracting layer 53.
Decorated by the metal ions, the photovoltaic efficiency of the electrode 5 is increased. When the nanometer crystal film 52 is coated on the transparent conductive substrate 51 via sintering at 200 to 600 degrees Celsius, abnormal accumulation often occurs so that the soaking of titanium dioxide in the dye is poor and that the expansion of the surface of the electrode 5 is limited. Hence, the photovoltaic efficiency is low.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.